Good question!

So in manual therapy there's this concept called the SAID principle - the idea that body tissue makes Specific Adaptations to Imposed Demands. The idea of "adaptations" is extremely broad - a muscle becoming progressively stronger as it's gradually exposed to greater & greater loads is the easiest example. (That idea of "sensitization" from my earlier response is also an example of this). The principle works in both directions, too - a strong muscle that's not regularly moving heavy loads will become smaller and weaker, saving on maintenance resources.

The other thing it's important to understand is that both our bodies, and the demands we make of them, are not symmetrical. You say you work an office job, meaning that you (presumably) work your mouse using your right hand, meaning the activity your right hand, arm, and upper back muscles are performing throughout the day are significantly different than those on the left. This could, over time, lead to increased sensations of pain and fatigue on that right side (and, again referring back to that idea of sensitization, that could mean your right side becomes more vulnerable to sensations of pain and fatigue). Muscles that are used more, thar experience a lot of pain and fatigue, will often have a higher "resting tone" - they're firmer when at rest.

Calling something a "knot" is useful shorthand - certainly easier than calling something "a region of skin and muscle that has become especially sensitive and painful due to various experiential and environmental factors working in concert over a fundamentally-unknowable length of time". For laypeople it's fine, it doesn't really make a difference - this stuff is more inside baseball for folks like me who need to actually think about the biomechanical realities underpinning the stuff we see on our tables.

Apologies for pulling out the comment, but as I was writing my reply I decided the response would probably be interesting in a general sense.

Sure - like I said, it's useful shorthand. If a patient tells me they feel a knot in their back, it gives me a pretty clear idea of what they're feeling, and it's not as though I'm going to scold them for using colloquial terminology. There's absolutely nothing wrong with someone saying they feel a knot in their back or a crick in their neck or pins and needles in their leg etc etc etc. That's just, like, language. The reasons I'm being precise about it are 1) I was asked, and 2) If overused, euphemism replaces more-correct knowledge in ways that are subtly but definitely harmful.

What do I mean by that second point? Well, the human "pain experience" is multifactoral. It used to be believed that all pain stemmed from physical dysfunction or damage - "issues in the tissues" AKA The Structural Model of pain. In the past couple decades, that's been getting supplanted by a new theory called The Biopsychosocial Model:

• "Bio": There is a definite physical, or biological, contributing factor to pain. Physical damage can and does create painful stimulus, and there are neurological signals and neurotransmitters that are positively linked to pain sensations.
• "Psycho": A person's mental state plays a significant role in their pain experience. Depression and anxiety have been shown to worsen pain symptoms across the board. Prolonged periods of stress are both physically and mentally taxing in ways that are severely deleterious to health. Trauma, grief, and emotional turmoil can all have unpredictable effects on a person's perception of pain.
• "Social": This one is a touch misleading. While social circumstances definitely play a role in a person's pain experience, it might be more accurate to call these "cultural" factors. For example: in American society, men are socially encouraged to be uncomplaining family providers who hold themselves aloof from expressions of vulnerability. Pain is to be ignored, "powered through", as is emotional turmoil. Seeking help is seen as a sign of weakness. What is that mindset going to do to a person's experience of pain? What effect might not having enough money to pay for both rent and medical treatment have on a person's pain? How would a person without close friends cope with pain?

What does that have to do with how we think about euphemisms like "knots"? Hopefully from that brief explanation of the BPS model of pain, you can see that we've come to appreciate that how a person THINKS about pain - what it represents, what it affects, how it might be addressed - can have an outsized effect on their actual PERCEPTION of that pain.

So: when someone says "Ugh, I have this terrible knot in my back", what might that represent? They might believe that a "knot" is a physical Thing, something that can be kneaded like clay or popped like a balloon. They might feel like this knot is something that happened TO them. They might not trust in their ability to address it without the aid of a professional. They might feel shame for allowing a knot to form in the first place, due to "bad posture" (not a real thing btw) or from not getting enough exercise or from having a "bad diet". They might start taking large amounts of rest in their free time, believing themselves to be at risk of injury otherwise. Every time they become aware of that knot, they might then have this goulash of fear, uncertainty, and shame swirling around that experience, worsening their perceived pain.

Conversely: a person feels a sensation of knotlike soreness in their mid-back. This person takes this pain as an indication that their body could use a change of position, possibly some light exercise, and they decide to get up from their chair, walk around, swing their arms from side to side. They might reflect that they slept poorly the night before, which is making them more sensitive to pain, and they might realize that stressful conversations with co-workers have been making them upset - these things are uncomfortable, certainly, but with these realizations come the knowledge that the work day will end and sleep will come.

In these two cases, who has a healthier relationship with their pain? The same pain is present at the outset, but the person who doesn't think euphemistically, who sees their pain as a form of useful, actionable feedback, as communication between their living body's diverse systems, is going to have a much easier time navigating their pain.

This probably feels like something of an exaggeration, and you wouldn't be wrong, but hopefully it's generally illustrative of why I like to push back against euphemistic language around pain.